Merge tag 'timers-core-2022-12-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer updates from Thomas Gleixner:
"Updates for timers, timekeeping and drivers:

Core:

- The timer_shutdown[_sync]() infrastructure:

Tearing down timers can be tedious when there are circular
dependencies to other things which need to be torn down. A prime
example is timer and workqueue where the timer schedules work and
the work arms the timer.

What needs to prevented is that pending work which is drained via
destroy_workqueue() does not rearm the previously shutdown timer.
Nothing in that shutdown sequence relies on the timer being
functional.

The conclusion was that the semantics of timer_shutdown_sync()
should be:
- timer is not enqueued
- timer callback is not running
- timer cannot be rearmed

Preventing the rearming of shutdown timers is done by discarding
rearm attempts silently.

A warning for the case that a rearm attempt of a shutdown timer is
detected would not be really helpful because it's entirely unclear
how it should be acted upon. The only way to address such a case is
to add 'if (in_shutdown)' conditionals all over the place. This is
error prone and in most cases of teardown not required all.

- The real fix for the bluetooth HCI teardown based on
timer_shutdown_sync().

A larger scale conversion to timer_shutdown_sync() is work in
progress.

- Consolidation of VDSO time namespace helper functions

- Small fixes for timer and timerqueue

Drivers:

- Prevent integer overflow on the XGene-1 TVAL register which causes
an never ending interrupt storm.

- The usual set of new device tree bindings

- Small fixes and improvements all over the place"

* tag 'timers-core-2022-12-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (34 commits)
dt-bindings: timer: renesas,cmt: Add r8a779g0 CMT support
dt-bindings: timer: renesas,tmu: Add r8a779g0 support
clocksource/drivers/arm_arch_timer: Use kstrtobool() instead of strtobool()
clocksource/drivers/timer-ti-dm: Fix missing clk_disable_unprepare in dmtimer_systimer_init_clock()
clocksource/drivers/timer-ti-dm: Clear settings on probe and free
clocksource/drivers/timer-ti-dm: Make timer_get_irq static
clocksource/drivers/timer-ti-dm: Fix warning for omap_timer_match
clocksource/drivers/arm_arch_timer: Fix XGene-1 TVAL register math error
clocksource/drivers/timer-npcm7xx: Enable timer 1 clock before use
dt-bindings: timer: nuvoton,npcm7xx-timer: Allow specifying all clocks
dt-bindings: timer: rockchip: Add rockchip,rk3128-timer
clockevents: Repair kernel-doc for clockevent_delta2ns()
clocksource/drivers/ingenic-ost: Define pm functions properly in platform_driver struct
clocksource/drivers/sh_cmt: Access registers according to spec
vdso/timens: Refactor copy-pasted find_timens_vvar_page() helper into one copy
Bluetooth: hci_qca: Fix the teardown problem for real
timers: Update the documentation to reflect on the new timer_shutdown() API
timers: Provide timer_shutdown[_sync]()
timers: Add shutdown mechanism to the internal functions
timers: Split [try_to_]del_timer[_sync]() to prepare for shutdown mode
...

Documentation/RCU/Design/Requirements/Requirements.rst

···
 one of its functions results in a segmentation fault. The module-unload
 functions must therefore cancel any delayed calls to loadable-module
 functions, for example, any outstanding mod_timer() must be dealt
-with via del_timer_sync() or similar.
+with via timer_shutdown_sync() or similar.
 
 Unfortunately, there is no way to cancel an RCU callback; once you
 invoke call_rcu(), the callback function is eventually going to be

Documentation/core-api/local_ops.rst

···
 
     static void __exit test_exit(void)
     {
-            del_timer_sync(&test_timer);
+            timer_shutdown_sync(&test_timer);
     }
 
     module_init(test_init);

Documentation/devicetree/bindings/timer/nuvoton,npcm7xx-timer.yaml

···
       - description: The timer interrupt of timer 0
 
   clocks:
-    maxItems: 1
+    items:
+      - description: The reference clock for timer 0
+      - description: The reference clock for timer 1
+      - description: The reference clock for timer 2
+      - description: The reference clock for timer 3
+      - description: The reference clock for timer 4
+    minItems: 1
 
 required:
   - compatible

Documentation/devicetree/bindings/timer/renesas,cmt.yaml

···
           - enum:
               - renesas,r8a779a0-cmt0     # 32-bit CMT0 on R-Car V3U
               - renesas,r8a779f0-cmt0     # 32-bit CMT0 on R-Car S4-8
+              - renesas,r8a779g0-cmt0     # 32-bit CMT0 on R-Car V4H
           - const: renesas,rcar-gen4-cmt0 # 32-bit CMT0 on R-Car Gen4
 
       - items:
           - enum:
               - renesas,r8a779a0-cmt1     # 48-bit CMT on R-Car V3U
               - renesas,r8a779f0-cmt1     # 48-bit CMT on R-Car S4-8
+              - renesas,r8a779g0-cmt1     # 48-bit CMT on R-Car V4H
           - const: renesas,rcar-gen4-cmt1 # 48-bit CMT on R-Car Gen4
 
   reg:

Documentation/devicetree/bindings/timer/renesas,tmu.yaml

···
           - renesas,tmu-r8a77995 # R-Car D3
           - renesas,tmu-r8a779a0 # R-Car V3U
           - renesas,tmu-r8a779f0 # R-Car S4-8
+          - renesas,tmu-r8a779g0 # R-Car V4H
       - const: renesas,tmu
 
   reg:

Documentation/devicetree/bindings/timer/rockchip,rk-timer.yaml

···
           - enum:
               - rockchip,rv1108-timer
               - rockchip,rk3036-timer
+              - rockchip,rk3128-timer
               - rockchip,rk3188-timer
               - rockchip,rk3228-timer
               - rockchip,rk3229-timer

Documentation/kernel-hacking/locking.rst

···
 
             while (list) {
                     struct foo *next = list->next;
-                    del_timer(&list->timer);
+                    timer_delete(&list->timer);
                     kfree(list);
                     list = next;
             }
···
 the element (which has already been freed!).
 
 This can be avoided by checking the result of
-del_timer(): if it returns 1, the timer has been deleted.
+timer_delete(): if it returns 1, the timer has been deleted.
 If 0, it means (in this case) that it is currently running, so we can
 do::
 
···
 
                     while (list) {
                             struct foo *next = list->next;
-                            if (!del_timer(&list->timer)) {
+                            if (!timer_delete(&list->timer)) {
                                     /* Give timer a chance to delete this */
                                     spin_unlock_bh(&list_lock);
                                     goto retry;
···
 Another common problem is deleting timers which restart themselves (by
 calling add_timer() at the end of their timer function).
 Because this is a fairly common case which is prone to races, you should
-use del_timer_sync() (``include/linux/timer.h``) to
-handle this case. It returns the number of times the timer had to be
-deleted before we finally stopped it from adding itself back in.
+use timer_delete_sync() (``include/linux/timer.h``) to handle this case.
+
+Before freeing a timer, timer_shutdown() or timer_shutdown_sync() should be
+called which will keep it from being rearmed. Any subsequent attempt to
+rearm the timer will be silently ignored by the core code.
+
 
 Locking Speed
 =============
···
 
 -  kfree()
 
--  add_timer() and del_timer()
+-  add_timer() and timer_delete()
 
 Mutex API reference
 ===================

Documentation/timers/hrtimers.rst

···
 was not really a win, due to the different data structures. Also, the
 hrtimer functions now have clearer behavior and clearer names - such as
 hrtimer_try_to_cancel() and hrtimer_cancel() [which are roughly
-equivalent to del_timer() and del_timer_sync()] - so there's no direct
+equivalent to timer_delete() and timer_delete_sync()] - so there's no direct
 1:1 mapping between them on the algorithmic level, and thus no real
 potential for code sharing either.
 

Documentation/translations/it_IT/kernel-hacking/locking.rst

···
 
             while (list) {
                     struct foo *next = list->next;
-                    del_timer(&list->timer);
+                    timer_delete(&list->timer);
                     kfree(list);
                     list = next;
             }
···
 di eliminare il suo oggetto (che però è già stato eliminato).
 
 Questo può essere evitato controllando il valore di ritorno di
-del_timer(): se ritorna 1, il temporizzatore è stato già
+timer_delete(): se ritorna 1, il temporizzatore è stato già
 rimosso. Se 0, significa (in questo caso) che il temporizzatore è in
 esecuzione, quindi possiamo fare come segue::
 
···
 
                     while (list) {
                             struct foo *next = list->next;
-                            if (!del_timer(&list->timer)) {
+                            if (!timer_delete(&list->timer)) {
                                     /* Give timer a chance to delete this */
                                     spin_unlock_bh(&list_lock);
                                     goto retry;
···
 Un altro problema è l'eliminazione dei temporizzatori che si riavviano
 da soli (chiamando add_timer() alla fine della loro esecuzione).
 Dato che questo è un problema abbastanza comune con una propensione
-alle corse critiche, dovreste usare del_timer_sync()
-(``include/linux/timer.h``) per gestire questo caso. Questa ritorna il
-numero di volte che il temporizzatore è stato interrotto prima che
-fosse in grado di fermarlo senza che si riavviasse.
+alle corse critiche, dovreste usare timer_delete_sync()
+(``include/linux/timer.h``) per gestire questo caso.
 
 Velocità della sincronizzazione
 ===============================
···
 
 -  kfree()
 
--  add_timer() e del_timer()
+-  add_timer() e timer_delete()
 
 Riferimento per l'API dei Mutex
 ===============================

Documentation/translations/zh_CN/core-api/local_ops.rst

···
 
     static void __exit test_exit(void)
     {
-            del_timer_sync(&test_timer);
+            timer_shutdown_sync(&test_timer);
     }
 
     module_init(test_init);

arch/arm/mach-spear/time.c

···
 		200, 16, clocksource_mmio_readw_up);
 }
 
-static inline void timer_shutdown(struct clock_event_device *evt)
+static inline void spear_timer_shutdown(struct clock_event_device *evt)
 {
 	u16 val = readw(gpt_base + CR(CLKEVT));
 
···
 
 static int spear_shutdown(struct clock_event_device *evt)
 {
-	timer_shutdown(evt);
+	spear_timer_shutdown(evt);
 
 	return 0;
 }
···
 	u16 val;
 
 	/* stop the timer */
-	timer_shutdown(evt);
+	spear_timer_shutdown(evt);
 
 	val = readw(gpt_base + CR(CLKEVT));
 	val |= CTRL_ONE_SHOT;
···
 	u16 val;
 
 	/* stop the timer */
-	timer_shutdown(evt);
+	spear_timer_shutdown(evt);
 
 	period = clk_get_rate(gpt_clk) / HZ;
 	period >>= CTRL_PRESCALER16;

arch/arm64/kernel/vdso.c

···
 	mmap_read_unlock(mm);
 	return 0;
 }
-
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops.
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-	WARN(1, "vvar_page accessed remotely");
-
-	return NULL;
-}
-#else
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	return NULL;
-}
 #endif
 
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,

arch/powerpc/kernel/vdso.c

···
 
 	return 0;
 }
-
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops.
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-	WARN(1, "vvar_page accessed remotely");
-
-	return NULL;
-}
-#else
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	return NULL;
-}
 #endif
 
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,

arch/riscv/kernel/vdso.c

···
 	mmap_read_unlock(mm);
 	return 0;
 }
-
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops.
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-	WARN(1, "vvar_page accessed remotely");
-
-	return NULL;
-}
-#else
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	return NULL;
-}
 #endif
 
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,

arch/s390/kernel/vdso.c

···
 	return (struct vdso_data *)(vvar_page);
 }
 
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops().
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-	WARN(1, "vvar_page accessed remotely");
-	return NULL;
-}
-
 /*
  * The VVAR page layout depends on whether a task belongs to the root or
  * non-root time namespace. Whenever a task changes its namespace, the VVAR
···
 	}
 	mmap_read_unlock(mm);
 	return 0;
-}
-#else
-static inline struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	return NULL;
 }
 #endif
 

arch/x86/entry/vdso/vma.c

···
 }
 
 #ifdef CONFIG_TIME_NS
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops().
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-
-	WARN(1, "vvar_page accessed remotely");
-
-	return NULL;
-}
-
 /*
  * The vvar page layout depends on whether a task belongs to the root or
  * non-root time namespace. Whenever a task changes its namespace, the VVAR
···
 	mmap_read_unlock(mm);
 
 	return 0;
-}
-#else
-static inline struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	return NULL;
 }
 #endif
 

drivers/bluetooth/hci_qca.c

···
 	skb_queue_purge(&qca->tx_wait_q);
 	skb_queue_purge(&qca->txq);
 	skb_queue_purge(&qca->rx_memdump_q);
+	/*
+	 * Shut the timers down so they can't be rearmed when
+	 * destroy_workqueue() drains pending work which in turn might try
+	 * to arm a timer.  After shutdown rearm attempts are silently
+	 * ignored by the timer core code.
+	 */
+	timer_shutdown_sync(&qca->tx_idle_timer);
+	timer_shutdown_sync(&qca->wake_retrans_timer);
 	destroy_workqueue(qca->workqueue);
-	del_timer_sync(&qca->tx_idle_timer);
-	del_timer_sync(&qca->wake_retrans_timer);
 	qca->hu = NULL;
 
 	kfree_skb(qca->rx_skb);

drivers/char/tpm/tpm-dev-common.c

···
 out:
 	if (!priv->response_length) {
 		*off = 0;
-		del_singleshot_timer_sync(&priv->user_read_timer);
+		del_timer_sync(&priv->user_read_timer);
 		flush_work(&priv->timeout_work);
 	}
 	mutex_unlock(&priv->buffer_mutex);
···
 void tpm_common_release(struct file *file, struct file_priv *priv)
 {
 	flush_work(&priv->async_work);
-	del_singleshot_timer_sync(&priv->user_read_timer);
+	del_timer_sync(&priv->user_read_timer);
 	flush_work(&priv->timeout_work);
 	file->private_data = NULL;
 	priv->response_length = 0;

drivers/clocksource/arm_arch_timer.c

···
 #include <linux/clocksource.h>
 #include <linux/clocksource_ids.h>
 #include <linux/interrupt.h>
+#include <linux/kstrtox.h>
 #include <linux/of_irq.h>
 #include <linux/of_address.h>
 #include <linux/io.h>
···
 
 static int __init early_evtstrm_cfg(char *buf)
 {
-	return strtobool(buf, &evtstrm_enable);
+	return kstrtobool(buf, &evtstrm_enable);
 }
 early_param("clocksource.arm_arch_timer.evtstrm", early_evtstrm_cfg);
 
···
 	return timer_handler(ARCH_TIMER_MEM_VIRT_ACCESS, evt);
 }
 
-static __always_inline int timer_shutdown(const int access,
-					  struct clock_event_device *clk)
+static __always_inline int arch_timer_shutdown(const int access,
+					       struct clock_event_device *clk)
 {
 	unsigned long ctrl;
 
···
 
 static int arch_timer_shutdown_virt(struct clock_event_device *clk)
 {
-	return timer_shutdown(ARCH_TIMER_VIRT_ACCESS, clk);
+	return arch_timer_shutdown(ARCH_TIMER_VIRT_ACCESS, clk);
 }
 
 static int arch_timer_shutdown_phys(struct clock_event_device *clk)
 {
-	return timer_shutdown(ARCH_TIMER_PHYS_ACCESS, clk);
+	return arch_timer_shutdown(ARCH_TIMER_PHYS_ACCESS, clk);
 }
 
 static int arch_timer_shutdown_virt_mem(struct clock_event_device *clk)
 {
-	return timer_shutdown(ARCH_TIMER_MEM_VIRT_ACCESS, clk);
+	return arch_timer_shutdown(ARCH_TIMER_MEM_VIRT_ACCESS, clk);
 }
 
 static int arch_timer_shutdown_phys_mem(struct clock_event_device *clk)
 {
-	return timer_shutdown(ARCH_TIMER_MEM_PHYS_ACCESS, clk);
+	return arch_timer_shutdown(ARCH_TIMER_MEM_PHYS_ACCESS, clk);
 }
 
 static __always_inline void set_next_event(const int access, unsigned long evt,

drivers/clocksource/ingenic-ost.c

···
 	return 0;
 }
 
-static int __maybe_unused ingenic_ost_suspend(struct device *dev)
+static int ingenic_ost_suspend(struct device *dev)
 {
 	struct ingenic_ost *ost = dev_get_drvdata(dev);
 
···
 	return 0;
 }
 
-static int __maybe_unused ingenic_ost_resume(struct device *dev)
+static int ingenic_ost_resume(struct device *dev)
 {
 	struct ingenic_ost *ost = dev_get_drvdata(dev);
 
 	return clk_enable(ost->clk);
 }
 
-static const struct dev_pm_ops __maybe_unused ingenic_ost_pm_ops = {
+static const struct dev_pm_ops ingenic_ost_pm_ops = {
 	/* _noirq: We want the OST clock to be gated last / ungated first */
 	.suspend_noirq = ingenic_ost_suspend,
 	.resume_noirq  = ingenic_ost_resume,
···
 static struct platform_driver ingenic_ost_driver = {
 	.driver = {
 		.name = "ingenic-ost",
-#ifdef CONFIG_PM_SUSPEND
-		.pm = &ingenic_ost_pm_ops,
-#endif
+		.pm = pm_sleep_ptr(&ingenic_ost_pm_ops),
 		.of_match_table = ingenic_ost_of_match,
 	},
 };

drivers/clocksource/sh_cmt.c

···
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/ioport.h>
 #include <linux/irq.h>
 #include <linux/module.h>
···
 	void __iomem *mapbase;
 	struct clk *clk;
 	unsigned long rate;
+	unsigned int reg_delay;
 
 	raw_spinlock_t lock; /* Protect the shared start/stop register */
 
···
 
 static inline void sh_cmt_write_cmstr(struct sh_cmt_channel *ch, u32 value)
 {
-	if (ch->iostart)
-		ch->cmt->info->write_control(ch->iostart, 0, value);
-	else
-		ch->cmt->info->write_control(ch->cmt->mapbase, 0, value);
+	u32 old_value = sh_cmt_read_cmstr(ch);
+
+	if (value != old_value) {
+		if (ch->iostart) {
+			ch->cmt->info->write_control(ch->iostart, 0, value);
+			udelay(ch->cmt->reg_delay);
+		} else {
+			ch->cmt->info->write_control(ch->cmt->mapbase, 0, value);
+			udelay(ch->cmt->reg_delay);
+		}
+	}
 }
 
 static inline u32 sh_cmt_read_cmcsr(struct sh_cmt_channel *ch)
···
 
 static inline void sh_cmt_write_cmcsr(struct sh_cmt_channel *ch, u32 value)
 {
-	ch->cmt->info->write_control(ch->ioctrl, CMCSR, value);
+	u32 old_value = sh_cmt_read_cmcsr(ch);
+
+	if (value != old_value) {
+		ch->cmt->info->write_control(ch->ioctrl, CMCSR, value);
+		udelay(ch->cmt->reg_delay);
+	}
 }
 
 static inline u32 sh_cmt_read_cmcnt(struct sh_cmt_channel *ch)
···
 	return ch->cmt->info->read_count(ch->ioctrl, CMCNT);
 }
 
-static inline void sh_cmt_write_cmcnt(struct sh_cmt_channel *ch, u32 value)
+static inline int sh_cmt_write_cmcnt(struct sh_cmt_channel *ch, u32 value)
 {
+	/* Tests showed that we need to wait 3 clocks here */
+	unsigned int cmcnt_delay = DIV_ROUND_UP(3 * ch->cmt->reg_delay, 2);
+	u32 reg;
+
+	if (ch->cmt->info->model > SH_CMT_16BIT) {
+		int ret = read_poll_timeout_atomic(sh_cmt_read_cmcsr, reg,
+						   !(reg & SH_CMT32_CMCSR_WRFLG),
+						   1, cmcnt_delay, false, ch);
+		if (ret < 0)
+			return ret;
+	}
+
 	ch->cmt->info->write_count(ch->ioctrl, CMCNT, value);
+	udelay(cmcnt_delay);
+	return 0;
 }
 
 static inline void sh_cmt_write_cmcor(struct sh_cmt_channel *ch, u32 value)
 {
-	ch->cmt->info->write_count(ch->ioctrl, CMCOR, value);
+	u32 old_value = ch->cmt->info->read_count(ch->ioctrl, CMCOR);
+
+	if (value != old_value) {
+		ch->cmt->info->write_count(ch->ioctrl, CMCOR, value);
+		udelay(ch->cmt->reg_delay);
+	}
 }
 
 static u32 sh_cmt_get_counter(struct sh_cmt_channel *ch, u32 *has_wrapped)
···
 
 static int sh_cmt_enable(struct sh_cmt_channel *ch)
 {
-	int k, ret;
+	int ret;
 
 	dev_pm_syscore_device(&ch->cmt->pdev->dev, true);
 
···
 	}
 
 	sh_cmt_write_cmcor(ch, 0xffffffff);
-	sh_cmt_write_cmcnt(ch, 0);
+	ret = sh_cmt_write_cmcnt(ch, 0);
 
-	/*
-	 * According to the sh73a0 user's manual, as CMCNT can be operated
-	 * only by the RCLK (Pseudo 32 kHz), there's one restriction on
-	 * modifying CMCNT register; two RCLK cycles are necessary before
-	 * this register is either read or any modification of the value
-	 * it holds is reflected in the LSI's actual operation.
-	 *
-	 * While at it, we're supposed to clear out the CMCNT as of this
-	 * moment, so make sure it's processed properly here.  This will
-	 * take RCLKx2 at maximum.
-	 */
-	for (k = 0; k < 100; k++) {
-		if (!sh_cmt_read_cmcnt(ch))
-			break;
-		udelay(1);
-	}
-
-	if (sh_cmt_read_cmcnt(ch)) {
+	if (ret || sh_cmt_read_cmcnt(ch)) {
 		dev_err(&ch->cmt->pdev->dev, "ch%u: cannot clear CMCNT\n",
 			ch->index);
 		ret = -ETIMEDOUT;
···
 
 static int sh_cmt_setup(struct sh_cmt_device *cmt, struct platform_device *pdev)
 {
-	unsigned int mask;
-	unsigned int i;
+	unsigned int mask, i;
+	unsigned long rate;
 	int ret;
 
 	cmt->pdev = pdev;
···
 	if (ret < 0)
 		goto err_clk_unprepare;
 
-	if (cmt->info->width == 16)
-		cmt->rate = clk_get_rate(cmt->clk) / 512;
-	else
-		cmt->rate = clk_get_rate(cmt->clk) / 8;
+	rate = clk_get_rate(cmt->clk);
+	if (!rate) {
+		ret = -EINVAL;
+		goto err_clk_disable;
+	}
+
+	/* We shall wait 2 input clks after register writes */
+	if (cmt->info->model >= SH_CMT_48BIT)
+		cmt->reg_delay = DIV_ROUND_UP(2UL * USEC_PER_SEC, rate);
+	cmt->rate = rate / (cmt->info->width == 16 ? 512 : 8);
 
 	/* Map the memory resource(s). */
 	ret = sh_cmt_map_memory(cmt);

drivers/clocksource/timer-npcm7xx.c

···
 
 static int __init npcm7xx_timer_init(struct device_node *np)
 {
+	struct clk *clk;
 	int ret;
 
 	ret = timer_of_init(np, &npcm7xx_to);
···
 	/* to the counter */
 	npcm7xx_to.of_clk.rate = npcm7xx_to.of_clk.rate /
 		(NPCM7XX_Tx_MIN_PRESCALE + 1);
+
+	/* Enable the clock for timer1, if it exists */
+	clk = of_clk_get(np, 1);
+	if (clk) {
+		if (!IS_ERR(clk))
+			clk_prepare_enable(clk);
+		else
+			pr_warn("%pOF: Failed to get clock for timer1: %pe", np, clk);
+	}
 
 	npcm7xx_clocksource_init();
 	npcm7xx_clockevents_init();

drivers/clocksource/timer-sp804.c

···
 	return IRQ_HANDLED;
 }
 
-static inline void timer_shutdown(struct clock_event_device *evt)
+static inline void evt_timer_shutdown(struct clock_event_device *evt)
 {
 	writel(0, common_clkevt->ctrl);
 }
 
 static int sp804_shutdown(struct clock_event_device *evt)
 {
-	timer_shutdown(evt);
+	evt_timer_shutdown(evt);
 	return 0;
 }
 
···
 	unsigned long ctrl = TIMER_CTRL_32BIT | TIMER_CTRL_IE |
 			     TIMER_CTRL_PERIODIC | TIMER_CTRL_ENABLE;
 
-	timer_shutdown(evt);
+	evt_timer_shutdown(evt);
 	writel(common_clkevt->reload, common_clkevt->load);
 	writel(ctrl, common_clkevt->ctrl);
 	return 0;

drivers/clocksource/timer-ti-dm-systimer.c

···
 		return error;
 
 	r = clk_get_rate(clock);
-	if (!r)
+	if (!r) {
+		clk_disable_unprepare(clock);
 		return -ENODEV;
+	}
 
 	if (is_ick)
 		t->ick = clock;

drivers/clocksource/timer-ti-dm.c

···
 static int omap_dm_timer_free(struct omap_dm_timer *cookie)
 {
 	struct dmtimer *timer;
+	struct device *dev;
+	int rc;
 
 	timer = to_dmtimer(cookie);
 	if (unlikely(!timer))
···
 
 	WARN_ON(!timer->reserved);
 	timer->reserved = 0;
+
+	dev = &timer->pdev->dev;
+	rc = pm_runtime_resume_and_get(dev);
+	if (rc)
+		return rc;
+
+	/* Clear timer configuration */
+	dmtimer_write(timer, OMAP_TIMER_CTRL_REG, 0);
+
+	pm_runtime_put_sync(dev);
+
 	return 0;
 }
 
-int omap_dm_timer_get_irq(struct omap_dm_timer *cookie)
+static int omap_dm_timer_get_irq(struct omap_dm_timer *cookie)
 {
 	struct dmtimer *timer = to_dmtimer(cookie);
 	if (timer)
···
 			goto err_disable;
 		}
 		__omap_dm_timer_init_regs(timer);
+
+		/* Clear timer configuration */
+		dmtimer_write(timer, OMAP_TIMER_CTRL_REG, 0);
+
 		pm_runtime_put(dev);
 	}
 
···
 	.remove = omap_dm_timer_remove,
 	.driver = {
 		.name   = "omap_timer",
-		.of_match_table = of_match_ptr(omap_timer_match),
+		.of_match_table = omap_timer_match,
 		.pm = &omap_dm_timer_pm_ops,
 	},
 };

drivers/staging/wlan-ng/hfa384x_usb.c

···
 		if (ctlx == get_active_ctlx(hw)) {
 			spin_unlock_irqrestore(&hw->ctlxq.lock, flags);
 
-			del_singleshot_timer_sync(&hw->reqtimer);
-			del_singleshot_timer_sync(&hw->resptimer);
+			del_timer_sync(&hw->reqtimer);
+			del_timer_sync(&hw->resptimer);
 			hw->req_timer_done = 1;
 			hw->resp_timer_done = 1;
 			usb_kill_urb(&hw->ctlx_urb);

drivers/staging/wlan-ng/prism2usb.c

···
 		 */
 		prism2sta_ifstate(wlandev, P80211ENUM_ifstate_disable);
 
-		del_singleshot_timer_sync(&hw->throttle);
-		del_singleshot_timer_sync(&hw->reqtimer);
-		del_singleshot_timer_sync(&hw->resptimer);
+		del_timer_sync(&hw->throttle);
+		del_timer_sync(&hw->reqtimer);
+		del_timer_sync(&hw->resptimer);
 
 		/* Unlink all the URBs. This "removes the wheels"
 		 * from the entire CTLX handling mechanism.

include/clocksource/timer-ti-dm.h

···
 struct omap_dm_timer {
 };
 
-int omap_dm_timer_get_irq(struct omap_dm_timer *timer);
-
 u32 omap_dm_timer_modify_idlect_mask(u32 inputmask);
 
 /*

include/linux/time_namespace.h

···
 void free_time_ns(struct time_namespace *ns);
 void timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk);
 struct vdso_data *arch_get_vdso_data(void *vvar_page);
+struct page *find_timens_vvar_page(struct vm_area_struct *vma);
 
 static inline void put_time_ns(struct time_namespace *ns)
 {
···
 				 struct task_struct *tsk)
 {
 	return;
+}
+
+static inline struct page *find_timens_vvar_page(struct vm_area_struct *vma)
+{
+	return NULL;
 }
 
 static inline void timens_add_monotonic(struct timespec64 *ts) { }

include/linux/timer.h

···
 }
 
 extern void add_timer_on(struct timer_list *timer, int cpu);
-extern int del_timer(struct timer_list * timer);
 extern int mod_timer(struct timer_list *timer, unsigned long expires);
 extern int mod_timer_pending(struct timer_list *timer, unsigned long expires);
 extern int timer_reduce(struct timer_list *timer, unsigned long expires);
···
 extern void add_timer(struct timer_list *timer);
 
 extern int try_to_del_timer_sync(struct timer_list *timer);
+extern int timer_delete_sync(struct timer_list *timer);
+extern int timer_delete(struct timer_list *timer);
+extern int timer_shutdown_sync(struct timer_list *timer);
+extern int timer_shutdown(struct timer_list *timer);
 
-#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
-  extern int del_timer_sync(struct timer_list *timer);
-#else
-# define del_timer_sync(t)		del_timer(t)
-#endif
+/**
+ * del_timer_sync - Delete a pending timer and wait for a running callback
+ * @timer:	The timer to be deleted
+ *
+ * See timer_delete_sync() for detailed explanation.
+ *
+ * Do not use in new code. Use timer_delete_sync() instead.
+ */
+static inline int del_timer_sync(struct timer_list *timer)
+{
+	return timer_delete_sync(timer);
+}
 
-#define del_singleshot_timer_sync(t) del_timer_sync(t)
+/**
+ * del_timer - Delete a pending timer
+ * @timer:	The timer to be deleted
+ *
+ * See timer_delete() for detailed explanation.
+ *
+ * Do not use in new code. Use timer_delete() instead.
+ */
+static inline int del_timer(struct timer_list *timer)
+{
+	return timer_delete(timer);
+}
 
 extern void init_timers(void);
 struct hrtimer;

include/linux/timerqueue.h

···
 {
 	struct rb_node *leftmost = rb_first_cached(&head->rb_root);
 
-	return rb_entry(leftmost, struct timerqueue_node, node);
+	return rb_entry_safe(leftmost, struct timerqueue_node, node);
 }
 
 static inline void timerqueue_init(struct timerqueue_node *node)

kernel/time/clockevents.c

···
 }
 
 /**
- * clockevents_delta2ns - Convert a latch value (device ticks) to nanoseconds
+ * clockevent_delta2ns - Convert a latch value (device ticks) to nanoseconds
  * @latch:	value to convert
  * @evt:	pointer to clock event device descriptor
  *

kernel/time/namespace.c

···
 	offset[CLOCK_BOOTTIME_ALARM]	= boottime;
 }
 
+struct page *find_timens_vvar_page(struct vm_area_struct *vma)
+{
+	if (likely(vma->vm_mm == current->mm))
+		return current->nsproxy->time_ns->vvar_page;
+
+	/*
+	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
+	 * through interfaces like /proc/$pid/mem or
+	 * process_vm_{readv,writev}() as long as there's no .access()
+	 * in special_mapping_vmops().
+	 * For more details check_vma_flags() and __access_remote_vm()
+	 */
+
+	WARN(1, "vvar_page accessed remotely");
+
+	return NULL;
+}
+
 /*
  * Protects possibly multiple offsets writers racing each other
  * and tasks entering the namespace.

kernel/time/timer.c

···
 	unsigned int idx = UINT_MAX;
 	int ret = 0;
 
-	BUG_ON(!timer->function);
+	debug_assert_init(timer);
 
 	/*
 	 * This is a common optimization triggered by the networking code - if
···
 		 * dequeue/enqueue dance.
 		 */
 		base = lock_timer_base(timer, &flags);
+		/*
+		 * Has @timer been shutdown? This needs to be evaluated
+		 * while holding base lock to prevent a race against the
+		 * shutdown code.
+		 */
+		if (!timer->function)
+			goto out_unlock;
+
 		forward_timer_base(base);
 
 		if (timer_pending(timer) && (options & MOD_TIMER_REDUCE) &&
···
 		}
 	} else {
 		base = lock_timer_base(timer, &flags);
+		/*
+		 * Has @timer been shutdown? This needs to be evaluated
+		 * while holding base lock to prevent a race against the
+		 * shutdown code.
+		 */
+		if (!timer->function)
+			goto out_unlock;
+
 		forward_timer_base(base);
 	}
 
···
 		/*
 		 * We are trying to schedule the timer on the new base.
 		 * However we can't change timer's base while it is running,
-		 * otherwise del_timer_sync() can't detect that the timer's
+		 * otherwise timer_delete_sync() can't detect that the timer's
 		 * handler yet has not finished. This also guarantees that the
 		 * timer is serialized wrt itself.
 		 */
···
 }
 
 /**
- * mod_timer_pending - modify a pending timer's timeout
- * @timer: the pending timer to be modified
- * @expires: new timeout in jiffies
+ * mod_timer_pending - Modify a pending timer's timeout
+ * @timer:	The pending timer to be modified
+ * @expires:	New absolute timeout in jiffies
  *
- * mod_timer_pending() is the same for pending timers as mod_timer(),
- * but will not re-activate and modify already deleted timers.
+ * mod_timer_pending() is the same for pending timers as mod_timer(), but
+ * will not activate inactive timers.
  *
- * It is useful for unserialized use of timers.
+ * If @timer->function == NULL then the start operation is silently
+ * discarded.
+ *
+ * Return:
+ * * %0 - The timer was inactive and not modified or was in
+ *	  shutdown state and the operation was discarded
+ * * %1 - The timer was active and requeued to expire at @expires
  */
 int mod_timer_pending(struct timer_list *timer, unsigned long expires)
 {
···
 EXPORT_SYMBOL(mod_timer_pending);
 
 /**
- * mod_timer - modify a timer's timeout
- * @timer: the timer to be modified
- * @expires: new timeout in jiffies
- *
- * mod_timer() is a more efficient way to update the expire field of an
- * active timer (if the timer is inactive it will be activated)
+ * mod_timer - Modify a timer's timeout
+ * @timer:	The timer to be modified
+ * @expires:	New absolute timeout in jiffies
  *
  * mod_timer(timer, expires) is equivalent to:
  *
  *     del_timer(timer); timer->expires = expires; add_timer(timer);
  *
+ * mod_timer() is more efficient than the above open coded sequence. In
+ * case that the timer is inactive, the del_timer() part is a NOP. The
+ * timer is in any case activated with the new expiry time @expires.
+ *
  * Note that if there are multiple unserialized concurrent users of the
  * same timer, then mod_timer() is the only safe way to modify the timeout,
  * since add_timer() cannot modify an already running timer.
  *
- * The function returns whether it has modified a pending timer or not.
- * (ie. mod_timer() of an inactive timer returns 0, mod_timer() of an
- * active timer returns 1.)
+ * If @timer->function == NULL then the start operation is silently
+ * discarded. In this case the return value is 0 and meaningless.
+ *
+ * Return:
+ * * %0 - The timer was inactive and started or was in shutdown
+ *	  state and the operation was discarded
+ * * %1 - The timer was active and requeued to expire at @expires or
+ *	  the timer was active and not modified because @expires did
+ *	  not change the effective expiry time
  */
 int mod_timer(struct timer_list *timer, unsigned long expires)
 {
···
 /**
  * timer_reduce - Modify a timer's timeout if it would reduce the timeout
  * @timer:	The timer to be modified
- * @expires:	New timeout in jiffies
+ * @expires:	New absolute timeout in jiffies
  *
  * timer_reduce() is very similar to mod_timer(), except that it will only
- * modify a running timer if that would reduce the expiration time (it will
- * start a timer that isn't running).
+ * modify an enqueued timer if that would reduce the expiration time. If
+ * @timer is not enqueued it starts the timer.
+ *
+ * If @timer->function == NULL then the start operation is silently
+ * discarded.
+ *
+ * Return:
+ * * %0 - The timer was inactive and started or was in shutdown
+ *	  state and the operation was discarded
+ * * %1 - The timer was active and requeued to expire at @expires or
+ *	  the timer was active and not modified because @expires
+ *	  did not change the effective expiry time such that the
+ *	  timer would expire earlier than already scheduled
  */
 int timer_reduce(struct timer_list *timer, unsigned long expires)
 {
···
 EXPORT_SYMBOL(timer_reduce);
 
 /**
- * add_timer - start a timer
- * @timer: the timer to be added
+ * add_timer - Start a timer
+ * @timer:	The timer to be started
  *
- * The kernel will do a ->function(@timer) callback from the
- * timer interrupt at the ->expires point in the future. The
- * current time is 'jiffies'.
+ * Start @timer to expire at @timer->expires in the future. @timer->expires
+ * is the absolute expiry time measured in 'jiffies'. When the timer expires
+ * timer->function(timer) will be invoked from soft interrupt context.
  *
- * The timer's ->expires, ->function fields must be set prior calling this
- * function.
+ * The @timer->expires and @timer->function fields must be set prior
+ * to calling this function.
  *
- * Timers with an ->expires field in the past will be executed in the next
- * timer tick.
+ * If @timer->function == NULL then the start operation is silently
+ * discarded.
+ *
+ * If @timer->expires is already in the past @timer will be queued to
+ * expire at the next timer tick.
+ *
+ * This can only operate on an inactive timer. Attempts to invoke this on
+ * an active timer are rejected with a warning.
  */
 void add_timer(struct timer_list *timer)
 {
-	BUG_ON(timer_pending(timer));
+	if (WARN_ON_ONCE(timer_pending(timer)))
+		return;
 	__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
 }
 EXPORT_SYMBOL(add_timer);
 
 /**
- * add_timer_on - start a timer on a particular CPU
- * @timer: the timer to be added
- * @cpu: the CPU to start it on
+ * add_timer_on - Start a timer on a particular CPU
+ * @timer:	The timer to be started
+ * @cpu:	The CPU to start it on
  *
- * This is not very scalable on SMP. Double adds are not possible.
+ * Same as add_timer() except that it starts the timer on the given CPU.
+ *
+ * See add_timer() for further details.
  */
 void add_timer_on(struct timer_list *timer, int cpu)
 {
 	struct timer_base *new_base, *base;
 	unsigned long flags;
 
-	BUG_ON(timer_pending(timer) || !timer->function);
+	debug_assert_init(timer);
+
+	if (WARN_ON_ONCE(timer_pending(timer)))
+		return;
 
 	new_base = get_timer_cpu_base(timer->flags, cpu);
 
···
 	 * wrong base locked.  See lock_timer_base().
 	 */
 	base = lock_timer_base(timer, &flags);
+	/*
+	 * Has @timer been shutdown? This needs to be evaluated while
+	 * holding base lock to prevent a race against the shutdown code.
+	 */
+	if (!timer->function)
+		goto out_unlock;
+
 	if (base != new_base) {
 		timer->flags |= TIMER_MIGRATING;
 
···
 
 	debug_timer_activate(timer);
 	internal_add_timer(base, timer);
+out_unlock:
 	raw_spin_unlock_irqrestore(&base->lock, flags);
 }
 EXPORT_SYMBOL_GPL(add_timer_on);
 
 /**
- * del_timer - deactivate a timer.
- * @timer: the timer to be deactivated
+ * __timer_delete - Internal function: Deactivate a timer
+ * @timer:	The timer to be deactivated
+ * @shutdown:	If true, this indicates that the timer is about to be
+ *		shutdown permanently.
  *
- * del_timer() deactivates a timer - this works on both active and inactive
- * timers.
+ * If @shutdown is true then @timer->function is set to NULL under the
+ * timer base lock which prevents further rearming of the time. In that
+ * case any attempt to rearm @timer after this function returns will be
+ * silently ignored.
  *
- * The function returns whether it has deactivated a pending timer or not.
- * (ie. del_timer() of an inactive timer returns 0, del_timer() of an
- * active timer returns 1.)
+ * Return:
+ * * %0 - The timer was not pending
+ * * %1 - The timer was pending and deactivated
  */
-int del_timer(struct timer_list *timer)
+static int __timer_delete(struct timer_list *timer, bool shutdown)
 {
 	struct timer_base *base;
 	unsigned long flags;
···
 
 	debug_assert_init(timer);
 
-	if (timer_pending(timer)) {
+	/*
+	 * If @shutdown is set then the lock has to be taken whether the
+	 * timer is pending or not to protect against a concurrent rearm
+	 * which might hit between the lockless pending check and the lock
+	 * aquisition. By taking the lock it is ensured that such a newly
+	 * enqueued timer is dequeued and cannot end up with
+	 * timer->function == NULL in the expiry code.
+	 *
+	 * If timer->function is currently executed, then this makes sure
+	 * that the callback cannot requeue the timer.
+	 */
+	if (timer_pending(timer) || shutdown) {
 		base = lock_timer_base(timer, &flags);
 		ret = detach_if_pending(timer, base, true);
+		if (shutdown)
+			timer->function = NULL;
 		raw_spin_unlock_irqrestore(&base->lock, flags);
 	}
 
 	return ret;
 }
-EXPORT_SYMBOL(del_timer);
 
 /**
- * try_to_del_timer_sync - Try to deactivate a timer
- * @timer: timer to delete
+ * timer_delete - Deactivate a timer
+ * @timer:	The timer to be deactivated
  *
- * This function tries to deactivate a timer. Upon successful (ret >= 0)
- * exit the timer is not queued and the handler is not running on any CPU.
+ * The function only deactivates a pending timer, but contrary to
+ * timer_delete_sync() it does not take into account whether the timer's
+ * callback function is concurrently executed on a different CPU or not.
+ * It neither prevents rearming of the timer.  If @timer can be rearmed
+ * concurrently then the return value of this function is meaningless.
+ *
+ * Return:
+ * * %0 - The timer was not pending
+ * * %1 - The timer was pending and deactivated
  */
-int try_to_del_timer_sync(struct timer_list *timer)
+int timer_delete(struct timer_list *timer)
+{
+	return __timer_delete(timer, false);
+}
+EXPORT_SYMBOL(timer_delete);
+
+/**
+ * timer_shutdown - Deactivate a timer and prevent rearming
+ * @timer:	The timer to be deactivated
+ *
+ * The function does not wait for an eventually running timer callback on a
+ * different CPU but it prevents rearming of the timer. Any attempt to arm
+ * @timer after this function returns will be silently ignored.
+ *
+ * This function is useful for teardown code and should only be used when
+ * timer_shutdown_sync() cannot be invoked due to locking or context constraints.
+ *
+ * Return:
+ * * %0 - The timer was not pending
+ * * %1 - The timer was pending
+ */
+int timer_shutdown(struct timer_list *timer)
+{
+	return __timer_delete(timer, true);
+}
+EXPORT_SYMBOL_GPL(timer_shutdown);
+
+/**
+ * __try_to_del_timer_sync - Internal function: Try to deactivate a timer
+ * @timer:	Timer to deactivate
+ * @shutdown:	If true, this indicates that the timer is about to be
+ *		shutdown permanently.
+ *
+ * If @shutdown is true then @timer->function is set to NULL under the
+ * timer base lock which prevents further rearming of the timer. Any
+ * attempt to rearm @timer after this function returns will be silently
+ * ignored.
+ *
+ * This function cannot guarantee that the timer cannot be rearmed
+ * right after dropping the base lock if @shutdown is false. That
+ * needs to be prevented by the calling code if necessary.
+ *
+ * Return:
+ * * %0  - The timer was not pending
+ * * %1  - The timer was pending and deactivated
+ * * %-1 - The timer callback function is running on a different CPU
+ */
+static int __try_to_del_timer_sync(struct timer_list *timer, bool shutdown)
 {
 	struct timer_base *base;
 	unsigned long flags;
···
 
 	if (base->running_timer != timer)
 		ret = detach_if_pending(timer, base, true);
+	if (shutdown)
+		timer->function = NULL;
 
 	raw_spin_unlock_irqrestore(&base->lock, flags);
 
 	return ret;
+}
+
+/**
+ * try_to_del_timer_sync - Try to deactivate a timer
+ * @timer:	Timer to deactivate
+ *
+ * This function tries to deactivate a timer. On success the timer is not
+ * queued and the timer callback function is not running on any CPU.
+ *
+ * This function does not guarantee that the timer cannot be rearmed right
+ * after dropping the base lock. That needs to be prevented by the calling
+ * code if necessary.
+ *
+ * Return:
+ * * %0  - The timer was not pending
+ * * %1  - The timer was pending and deactivated
+ * * %-1 - The timer callback function is running on a different CPU
+ */
+int try_to_del_timer_sync(struct timer_list *timer)
+{
+	return __try_to_del_timer_sync(timer, false);
 }
 EXPORT_SYMBOL(try_to_del_timer_sync);
 
···
 static inline void del_timer_wait_running(struct timer_list *timer) { }
 #endif
 
-#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 /**
- * del_timer_sync - deactivate a timer and wait for the handler to finish.
- * @timer: the timer to be deactivated
+ * __timer_delete_sync - Internal function: Deactivate a timer and wait
+ *			 for the handler to finish.
+ * @timer:	The timer to be deactivated
+ * @shutdown:	If true, @timer->function will be set to NULL under the
+ *		timer base lock which prevents rearming of @timer
  *
- * This function only differs from del_timer() on SMP: besides deactivating
- * the timer it also makes sure the handler has finished executing on other
- * CPUs.
+ * If @shutdown is not set the timer can be rearmed later. If the timer can
+ * be rearmed concurrently, i.e. after dropping the base lock then the
+ * return value is meaningless.
  *
- * Synchronization rules: Callers must prevent restarting of the timer,
- * otherwise this function is meaningless. It must not be called from
- * interrupt contexts unless the timer is an irqsafe one. The caller must
- * not hold locks which would prevent completion of the timer's
- * handler. The timer's handler must not call add_timer_on(). Upon exit the
- * timer is not queued and the handler is not running on any CPU.
+ * If @shutdown is set then @timer->function is set to NULL under timer
+ * base lock which prevents rearming of the timer. Any attempt to rearm
+ * a shutdown timer is silently ignored.
  *
- * Note: For !irqsafe timers, you must not hold locks that are held in
- *   interrupt context while calling this function. Even if the lock has
- *   nothing to do with the timer in question.  Here's why::
+ * If the timer should be reused after shutdown it has to be initialized
+ * again.
  *
- *    CPU0                             CPU1
- *    ----                             ----
- *                                     <SOFTIRQ>
- *                                       call_timer_fn();
- *                                       base->running_timer = mytimer;
- *    spin_lock_irq(somelock);
- *                                     <IRQ>
- *                                        spin_lock(somelock);
- *    del_timer_sync(mytimer);
- *    while (base->running_timer == mytimer);
- *
- * Now del_timer_sync() will never return and never release somelock.
- * The interrupt on the other CPU is waiting to grab somelock but
- * it has interrupted the softirq that CPU0 is waiting to finish.
- *
- * The function returns whether it has deactivated a pending timer or not.
+ * Return:
+ * * %0	- The timer was not pending
+ * * %1	- The timer was pending and deactivated
  */
-int del_timer_sync(struct timer_list *timer)
+static int __timer_delete_sync(struct timer_list *timer, bool shutdown)
 {
 	int ret;
 
···
 	 * don't use it in hardirq context, because it
 	 * could lead to deadlock.
 	 */
-	WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
+	WARN_ON(in_hardirq() && !(timer->flags & TIMER_IRQSAFE));
 
 	/*
 	 * Must be able to sleep on PREEMPT_RT because of the slowpath in
···
 		lockdep_assert_preemption_enabled();
 
 	do {
-		ret = try_to_del_timer_sync(timer);
+		ret = __try_to_del_timer_sync(timer, shutdown);
 
 		if (unlikely(ret < 0)) {
 			del_timer_wait_running(timer);
···
 
 	return ret;
 }
-EXPORT_SYMBOL(del_timer_sync);
-#endif
+
+/**
+ * timer_delete_sync - Deactivate a timer and wait for the handler to finish.
+ * @timer:	The timer to be deactivated
+ *
+ * Synchronization rules: Callers must prevent restarting of the timer,
+ * otherwise this function is meaningless. It must not be called from
+ * interrupt contexts unless the timer is an irqsafe one. The caller must
+ * not hold locks which would prevent completion of the timer's callback
+ * function. The timer's handler must not call add_timer_on(). Upon exit
+ * the timer is not queued and the handler is not running on any CPU.
+ *
+ * For !irqsafe timers, the caller must not hold locks that are held in
+ * interrupt context. Even if the lock has nothing to do with the timer in
+ * question.  Here's why::
+ *
+ *    CPU0                             CPU1
+ *    ----                             ----
+ *                                     <SOFTIRQ>
+ *                                       call_timer_fn();
+ *                                       base->running_timer = mytimer;
+ *    spin_lock_irq(somelock);
+ *                                     <IRQ>
+ *                                        spin_lock(somelock);
+ *    timer_delete_sync(mytimer);
+ *    while (base->running_timer == mytimer);
+ *
+ * Now timer_delete_sync() will never return and never release somelock.
+ * The interrupt on the other CPU is waiting to grab somelock but it has
+ * interrupted the softirq that CPU0 is waiting to finish.
+ *
+ * This function cannot guarantee that the timer is not rearmed again by
+ * some concurrent or preempting code, right after it dropped the base
+ * lock. If there is the possibility of a concurrent rearm then the return
+ * value of the function is meaningless.
+ *
+ * If such a guarantee is needed, e.g. for teardown situations then use
+ * timer_shutdown_sync() instead.
+ *
+ * Return:
+ * * %0	- The timer was not pending
+ * * %1	- The timer was pending and deactivated
+ */
+int timer_delete_sync(struct timer_list *timer)
+{
+	return __timer_delete_sync(timer, false);
+}
+EXPORT_SYMBOL(timer_delete_sync);
+
+/**
+ * timer_shutdown_sync - Shutdown a timer and prevent rearming
+ * @timer: The timer to be shutdown
+ *
+ * When the function returns it is guaranteed that:
+ *   - @timer is not queued
+ *   - The callback function of @timer is not running
+ *   - @timer cannot be enqueued again. Any attempt to rearm
+ *     @timer is silently ignored.
+ *
+ * See timer_delete_sync() for synchronization rules.
+ *
+ * This function is useful for final teardown of an infrastructure where
+ * the timer is subject to a circular dependency problem.
+ *
+ * A common pattern for this is a timer and a workqueue where the timer can
+ * schedule work and work can arm the timer. On shutdown the workqueue must
+ * be destroyed and the timer must be prevented from rearming. Unless the
+ * code has conditionals like 'if (mything->in_shutdown)' to prevent that
+ * there is no way to get this correct with timer_delete_sync().
+ *
+ * timer_shutdown_sync() is solving the problem. The correct ordering of
+ * calls in this case is:
+ *
+ *	timer_shutdown_sync(&mything->timer);
+ *	workqueue_destroy(&mything->workqueue);
+ *
+ * After this 'mything' can be safely freed.
+ *
+ * This obviously implies that the timer is not required to be functional
+ * for the rest of the shutdown operation.
+ *
+ * Return:
+ * * %0 - The timer was not pending
+ * * %1 - The timer was pending
+ */
+int timer_shutdown_sync(struct timer_list *timer)
+{
+	return __timer_delete_sync(timer, true);
+}
+EXPORT_SYMBOL_GPL(timer_shutdown_sync);
 
 static void call_timer_fn(struct timer_list *timer,
 			  void (*fn)(struct timer_list *),
···
 #endif
 	/*
 	 * Couple the lock chain with the lock chain at
-	 * del_timer_sync() by acquiring the lock_map around the fn()
-	 * call here and in del_timer_sync().
+	 * timer_delete_sync() by acquiring the lock_map around the fn()
+	 * call here and in timer_delete_sync().
 	 */
 	lock_map_acquire(&lockdep_map);
 
···
 		detach_timer(timer, true);
 
 		fn = timer->function;
+
+		if (WARN_ON_ONCE(!fn)) {
+			/* Should never happen. Emphasis on should! */
+			base->running_timer = NULL;
+			continue;
+		}
 
 		if (timer->flags & TIMER_IRQSAFE) {
 			raw_spin_unlock(&base->lock);
···
 	timer_setup_on_stack(&timer.timer, process_timeout, 0);
 	__mod_timer(&timer.timer, expire, MOD_TIMER_NOTPENDING);
 	schedule();
-	del_singleshot_timer_sync(&timer.timer);
+	del_timer_sync(&timer.timer);
 
 	/* Remove the timer from the object tracker */
 	destroy_timer_on_stack(&timer.timer);
···
 	struct timer_base *new_base;
 	int b, i;
 
-	BUG_ON(cpu_online(cpu));
-
 	for (b = 0; b < NR_BASES; b++) {
 		old_base = per_cpu_ptr(&timer_bases[b], cpu);
 		new_base = get_cpu_ptr(&timer_bases[b]);
···
 		 */
 		forward_timer_base(new_base);
 
-		BUG_ON(old_base->running_timer);
+		WARN_ON_ONCE(old_base->running_timer);
+		old_base->running_timer = NULL;
 
 		for (i = 0; i < WHEEL_SIZE; i++)
 			migrate_timer_list(new_base, old_base->vectors + i);

net/sunrpc/xprt.c

···
 	spin_unlock(&xprt->queue_lock);
 
 	/* Turn off autodisconnect */
-	del_singleshot_timer_sync(&xprt->timer);
+	del_timer_sync(&xprt->timer);
 	return 0;
 }